To improve management of docker-gbsyncd-vs. gbsyncd_startup.py simply spawned syncd processes and then exited. In that case, supervisord would no longer manage any processes in the container, and thus there was no way to know if a critical process had exited.
I recently created gbsyncdmgrd to be a more complete, robust replacement for gbsyncd_startup.py.
NOTE: This PR is dependent on the inclusion of gbsyncdmgrd in the sonic-sairedis repo. A submodule update is pending at
#7089
b512394398